The proposed investigation is designed to yield structural and functional information about the regulation of gene expression in the bacteriophage T7. This relatively simple organism has been chosen for my study since detailed descriptions of protein - nucleic acid - nucleic acid interactions are still most tractable in prokaryotes. Particularly advantageous is the fact that the T7 RNA polymerase is a single-subunit enzyme (mw 107 K), which recognizes highly conserved promoter sequences on T7 DNA. Specifically I intend to construct a molecular clone containing the T7 RNA polymerase gene, thereby facilitating the purification and stabilization of the protein. This will allow me to examine the biochemical and physical properties of the T7 RNA polymerase and the T7 RNA polymerase-promoter complex. I shall attempt to obtain crystals of the polymerase suitable for X-ray crystallographic analysis. A study of the functional differences between the two Classes of T7 RNA polymerase promoters will be undertaken. The mechanism of transcription termination and termination readthrough by T7 RNA polymerase will be compared to those of the E. coli RNA polymerase. Analyses of RNA structural interactions in T7 late and early mRNAs will examine the influence of these interactions on the functional efficiencies of messenger RNA.